4of22Rescuers see to0 the care of a patient in Kumamoto after an earthquake. The powerful temblor struck southern Japan barely 24 hours after a smaller quake hit the same region.Photo: Yusuke Ogata /Kyodo News

12of22A patient is evacuated by emergency staff from an hospital in Kumamoto City on April 16, 2016, over fears it could collapse as a wave of aftershocks shook the area. A powerful earthquake hit southern Japan early on April 16, 2016, authorities said, sending panicked residents from their homes and damaging buildings in a region where nerves were already frayed by a swarm of strong shaking. The earthquake hit just over a day after another strong tremor in the same area killed nine people, injured hundreds and toppled buildings. / AFP PHOTO / KAZUHIRO NOGIKAZUHIRO NOGI/AFP/Getty ImagesPhoto: KAZUHIRO NOGI, Stringer / AFP/Getty Images

13of22A patient is evacuated by emergency staff to an hospital in Kumamoto City on April 16, 2016. A strong 7,0 earthquake hit southern Japan early, the US Geological Survey said, a day after another powerful tremor killed at least nine people in the same area. Tens of thousands of people fled their homes after the 6.5-magnitude quake struck the southwestern island of Kyushu on Thursday night, leaving lumps of concrete strewn in the streets. / AFP PHOTO / KAZUHIRO NOGIKAZUHIRO NOGI/AFP/Getty ImagesPhoto: KAZUHIRO NOGI, Stringer / AFP/Getty Images

14of22MASHIKI, JAPAN - APRIL 16: People get up right after the 7.3 magnitude earthquak at the evacuation center at the Mashiki Town Gymnasium on April 16, 2016 in Mashiki, Kumamoto, Japan. A 7.3 magnitude earthquake hit Kumamoto prefecture once again on April 16, 2016 after the 6.4 earthquake on April 14, 2016 killed nine people. (Photo by Taro Karibe/Getty Images)Photo: Taro Karibe, Stringer / Getty Images

15of22MASHIKI, JAPAN - APRIL 16: A road newly damaged by the 7.3 magnitude earthquake is seen on April 16, 2016 in Mashiki, Kumamoto, Japan. A 7.3 magnitude earthquake hit Kumamoto prefecture once again on April 16, 2016 after the 6.4 earthquake on April 14, 2016 killed nine people. (Photo by Taro Karibe/Getty Images)Photo: Taro Karibe, Stringer / Getty Images

16of22One of the stone walls of Kumamoto Castle is damaged by Friday’s earthquake. The castle is a major tourism destination and one of the country’s designated Important Cultural Properties.Photo: Masterpress /Getty Images

17of22MASHIKI, JAPAN - APRIL 16: The rescue workers take care of an elderly woman suffering from the shock after the 7.3 magnitude earthquake at the evacuation center at the Mashiki Town Gymnasium on April 16, 2016 in Mashiki, Kumamoto, Japan. A 7.3 magnitude earthquake hit Kumamoto prefecture once again on April 16, 2016 after the 6.4 earthquake on April 14, 2016 killed nine people. (Photo by Taro Karibe/Getty Images)Photo: Taro Karibe, Stringer / Getty Images

18of22Evactuated residents wait at a park in Higashi-ku in Kumamoto City on April 16, 2016. A strong 7,0 earthquake hit southern Japan early, the US Geological Survey said, a day after another powerful tremor killed at least nine people in the same area. Tens of thousands of people fled their homes after the 6.5-magnitude quake struck the southwestern island of Kyushu on Thursday night, leaving lumps of concrete strewn in the streets. / AFP PHOTO / KAZUHIRO NOGIKAZUHIRO NOGI/AFP/Getty ImagesPhoto: KAZUHIRO NOGI, Stringer / AFP/Getty Images

20of22KUMAMOTO, JAPAN - APRIL 15: Members of the Japan Self-Defense Forces make rice balls at the soup-run operated at the evacuation center a day after the 2016 Kumamoto Earthquake at the Mashiki Town Hall on April 15, 2016 in Mashiki, Kumamoto, Japan. As of April 15 morning, at least nine people died in the powerful earthquake with a preliminary magnitude of 6.4 that struck Kumamoto Prefecture on April 14, 2016. (Photo by Masterpress/Getty Images)Photo: Masterpress, Stringer / Getty Images

22of22MASHIKI, JAPAN - APRIL 15: People charge mobile phones at the evacuation center one day after the 2016 Kumamoto Earthquake at the Mashiki Town Hall on April 15, 2016 in Mashiki, Kumamoto, Japan. As of April 15 morning, at least nine people died in the powerful earthquake with a preliminary magnitude of 6.4 that struck Kumamoto Prefecture on April 14, 2016. (Photo by Masterpress/Getty Images)Photo: Masterpress, Stringer / Getty Images

MASHIKI, Japan — A powerful earthquake with a preliminary magnitude of 7.3 struck San Antonio’s sister city in southern Japan barely 24 hours after a smaller quake hit the same region and killed 10 people.

At least six people were killed in the lastest quake, and authorities said hundreds of calls had come in from residents reporting people trapped inside houses and buildings. The Fire and Disaster Management Agency said 66 people were trapped inside a nursing home in Mashiki, the hardest-hit town, and rescue efforts were underway.

Mashiki is a suburb of Kumamoto, one of San Antonio’s nine sister cities around the world.

More than 400 people were treated at hospitals, but most of their injuries were not life-threatening, the Japanese broadcaster NHK said, citing its own tally. Video showed a resident, apparently rescued from underneath a collapsed house, on a stretcher being taken to a hospital by ambulance.

Meanwhile, the Kumamoto prefecture reported that a 10th person had died in the 6.5 magnitude quake that struck late Thursday.

Several aftershocks followed the quake that shook the Kumamoto region today. Japan’s Meteorological Agency issued an advisory for a tsunami up to 3 feet high along the coast west of the epicenter in Kumamoto, but it was lifted less than an hour later.

The agency upgraded the magnitude to 7.3 from an initial reading of 7.1.

Thursday’s weaker magnitude 6.5 earthquake brought down buildings and injured about 800 people, in addition to the 10 deaths. The epicenter of Friday’s earthquake was 8 miles northwest of Thursday’s and, at a depth of 6 miles, was shallower.

Because Friday’s quake was bigger, Thursday’s was technically a foreshock, Gen Aoki, an official with the meteorological agency told a news conference.

Chief Cabinet Secretary Yoshihide Suga, in an emergency news conference, said more than 300 calls came in to the Kumamoto police and 100 more to police in nearby Oita, seeking help and reporting people trapped or buried underneath debris.

Prime Minister Shinzo Abe, looking tired, said damage from the latest quake could be “extensive” and urged rescue workers to do their utmost to help those trapped in the rubble.

Sirens of patrol vehicles could be heard in the background as new crews reported from Mashiki. The asphalt outside the town hall had a new crack, apparently made by the latest earthquake. In nearby Uto City, police reported that City Hall appeared to be unsafe because of structural damage.

The Nuclear Regulation Authority said no abnormalities were found at the Sendai nuclear plant, where the only two of Japan’s 43 reactors are online. News video showed stones tumbled from the walls of historic Kumamoto Castle, and a wooden structure in the complex was smashed, adding to damage from Thursday’s quake.

At the Ark Hotel, east of the castle, hotel guests woke up to strong shaking and a warning siren. Hotel staff told guests, including tourists and journalists covering the quake, to evacuate their rooms and gather in the lobby for safety.

Friday’s temblor hit residents who were still in shock from the previous night’s quake and had suffered through more than 100 aftershocks in the interim.

Yuichiro Yoshikado said Thursday’s quake stuck as he was taking a bath in his apartment in Mashiki.

“I grabbed onto the sides of the bathtub, but the water in the tub, it was about 70 percent filled with water, was going like this,” he said, waving his arms, “and all the water splashed out.”

“It’s as if all control was lost. I thought I was going to die, and I couldn’t bear it any longer.”

A bright spot, broadcast repeatedly on TV, was the rescue of an apparently uninjured baby, from the rubble of a collapsed home.